Proximity rapid thermal diffusion (RTD) using arsenic has been used for doping high aspect ratio trench capacitors which may be used in high density dynamic memories. Nonuniformity of doping has been observed in SEM analyses at the trench comers after preferential etching used for junction delineation. Severe thinning was seen at the bottom comers of the junctions produced at low temperatures for long times (90 sec). This non- uniformity was alleviated at high diffusion temperatures for short time resulting in very uniform junctions. We modeled diffusion processes for trench doping using a process simulator, TSUPREM-IV. Default program data produced large discrepancies with experimental results and a new set of parameters was derived. The stress model in the oxide growth was incorporated in our calculations of the diffusion profiles to simulate formation of the dopant glass and obtain match with the experimental results.